1. Field of the Invention
The present invention relates to an optical disk reproducing device for reproducing information recorded on an optical disk. In particular, the present invention relates to a process for discriminating a type of an optical disk loaded to the optical disk reproducing device.
2. Description of Related Art
Recently, a digital versatile disk (DVD) that is an optical disk capable of recording and reproducing a large quantity of video and audio information than a compact disc (CD) has become commonplace. The DVD is in the limelight as a recording medium in the next generation because it has good image quality of pictures to be reproduced. There are several types of the DVD includes a DVD-ROM that stores information recorded on a manufacture's side and cannot be rewritten on a user's side, a DVD-R and a DVD+R on which information can be written only once on the user's side, and a DVD-RW, a DVD+RW and a DVD-RAM on which information can be rewritten a predetermined number of times on the user's side.
There is known a conventional technique of an optical disk discriminating device as disclosed in JP-A-2004-46977, for example. This device is used for discriminating a DVD-RAM from the various types of DVD described above when the DVD-RAM is loaded to an optical disk reproducing device. This optical disk discriminating device determines that the loaded optical disk is the DVD-RAM by detecting address pit (CAPA) from the number of times and an interval of short pulse signals obtained by a binary process performed on a total reflection sum signal obtained from reflection light received by an optical pickup.
In addition, JP-A-2005-38514 discloses another conventional technique of the optical disk discriminating device. The device detects a peak value and a bottom value of the total reflection sum signal obtained from the reflection light received by the optical pickup, and it compares a difference quantity between them with a reference level for detecting the address pit (CAPA) so as to determine whether or not the optical disk is the DVD-RAM.
In addition, JP-A-2000-285582 discloses another conventional technique of the optical disk discriminating device and method. The device or the method detects an RF signal read out from the disk in an off-track state in which only focusing prior to tracking control is performed, so that an amplitude of a generated envelope signal is detected. Further, the amplitude of the envelope signal is compared with a reference level. Based on a result of this comparison, it is determined whether or not the optical disk is the DVD-RAM.
However, the conventional technique disclosed in JP-A-2004-46977 has a following disadvantage. As described above, this technique detects the address pit (CAPA) from the number of times and an interval of short pulse signals obtained by a binary process performed on a total reflection sum signal. Because of a variation in an amplitude of an output signal of the optical pickup, a variation of reflectance of the optical disk or a variation of gain in a total reflection sum signal generating portion, an amplitude of the total reflection sum signal outputted from the total reflection sum signal generating portion may be varied. As a result, it becomes difficult to detect the address pit (CAPA) correctly since the binary process of the total reflection sum signal becomes hard to perform correctly. In this case, it may be difficult to discriminate the DVD-RAM correctly.
The conventional technique disclosed in JP-A-2005-38514 detects a peak value and a bottom value of the total reflection sum signal as described above, and it compares a difference quantity between them with a reference level for detecting the address pit (CAPA). In this case too, an amplitude of the total reflection sum signal outputted from the total reflection sum signal generating portion may be varied due to a variation in an amplitude of an output signal of the optical pickup, a variation in a reflectance of the optical disk or a variation in a gain in a total reflection sum signal generating portion. As a result, it becomes difficult to compare a difference quantity between a peak value and a bottom value of the total reflection sum signal with the reference level correctly, and it becomes difficult to detect the address pit (CAPA) correctly. In this case too, it may be difficult to discriminate the DVD-RAM correctly.
In addition, the conventional technique disclosed in JP-A-2000-285582 detects an amplitude of the envelope signal generated by detecting the RF signal as described above, and it further compares the amplitude of the envelope signal with a reference level so as to determine whether or not the optical disk is the DVD-RAM based on a result of the comparison. If there is a variation in the amplitude of the output signal from the optical pickup, a variation in a reflectance of the optical disk or a variation in a gain in the RF amplifier, an amplitude of the envelope signal may vary so that reliability of the result of the comparison with the reference level may be lowered. As a result, it may be difficult to determine that the optical disk is the DVD-RAM correctly.